Don't make the rookie error of ignoring or undertraining your back because you can't see it all that well in the mirror.
Trust me: building up the front of your deltoids to button-popping levels while leaving your back withering on the vine is a shortcut to an unbalanced physique and injury. Train your back 1-3 times per week with pulling movements as per this workout. Do 3 sets of each of these 3 moves, aiming for between 8-12 reps per set and 60 seconds rest between sets.
Single Arm Row
Get your upper body parallel with the floor by placing your left knee and left hand on a bench. With your right arm hanging at full extension, row a loaded dumbbell to your ribs, squeezing your latissimus dorsi muscle (aka the bat wing) throughout. Repeat on the other side.
Wide-Grip Bent Over Row
Holding a loaded barbell in front of you, hinge forward from your hips, keeping your abs and glutes braced. Row the barbell up to your ribs, pausing at the top to squeeze the scapula. Lower under control to a dead hang.
With light dumbbells held in a neutral grip in each hand, hinge forward at the hips, again keeping your abs and glutes locked. With a slight bend in your elbows, bring the weights back and out until your scapula is fully contracted. Lower under control.